1. FIELD OF THE INVENTION
The present inention relates generally to a sheet holding apparatus which is for holding a sheet such as a printed wiring board or the like, and especially to a sheet holding apparatus wherein the sheet holding position is easily, efficiently and precisely changeable responding to the change of the sheet metal size.
2. DESCRIPTION OF THE PRIOR ART
The conventional sheet holding apparatus is constructed as shown in FIG. 1 and FIG. 2. Rails 4 and 5 are fixed on a table 1 by putting blocks 2 and 3 by screw bolts 6 inbetween. A shaft 7 is rotatably held on the block 3, and a driving lever 8 is connected with an end part of the shaft 7, so as to receive an external force. Guide holders 9 are fixed on the shaft 7 by screw bolts 12. On the tip part of the guide holders 9, positioning guide pins 10 are fixed. In normal state the guide holders 9 are horizontally supported by springs 13, and at the same time the positioning guide pins 10 are vertically supported.
In the sheet metal holding apparatus shown in FIG. 1 and FIG. 2, when the external force is given on the driving lever 8, the shaft 7 and the guide holders 9 are rotated counterclockwise as shown in FIG. 2, so the positioning guide pins 10 are put down below a level of a carrying plane 15 of sheet 14. The sheet 14 is brought in as shown by arrow mark in FIG. 1 by a cylinder, a belt, a chain or the like known transfer means which are not drawn in figures, and the sheet 14 is stopped at the position which is shown in FIG. 1. Next, by taking off the external force from the driving lever 8, the shaft 7 and the guide holders 9 are rotated clockwise, and the positioning guide pins 10 are inserted into holes 16 of the sheet 14 to hold the latter at a predetermined position as shown in FIG. 1.
However, in case of changing for different size of the sheet 14, the distance between the rails 4 and 5, and the distance between each guide holders 9 must be changed.
Recently, a mode of manufacturing of many kinds but fewer number become popular, changing the sizes of the sheet becomes more frequent. In case of using the conventional apparatus, the manufacturing operation must be stopped and the holding position is necessary to adjust by human hands. So it becomes a problem that operation efficiency of the apparatus in manufacturing goes down.